Silver base alloy



35 ferred to zinc.

Patented Oct. 27, 1936 UNITED STATES OFFIC Kenneth L. Emmert,.lndianapolis, Ind assignor to P. R. Mallory & 00., Inc., Indianapolis, 11111., a corporation of Delaware No Drawing. Application an. 30', 1936;

'. 1 Serial No. 88,115

8 Claims. (01. 15-113) This invention relates to alloys and more particularly to alloys suitable for electrical contacts and the like.

An object of the invention is to produce an improved silver base alloy.

Another object is to provide an improved alloy for contacts. j j

A further object is to produce an improved electrical contact.

Other objects of the invention will be apparent from the following description taken in connection with the appended claims.

The present invention comprises the combination of elements, methods of manufacture, and the product thereof brought out and exemplified in the disclosure hereinafter set forth, the scope of the invention being indicated in the appended claims. v

While a preferred embodiment of the invention is'described herein, it is contemplated that considerable variation may be made in the method of procedure and the combination of elements without departing fromthe spirit of the invention.

According to the present invention an improved alloy is contemplated having the following ingredients present in substantially the ranges of proportions given below:

Percent Palladium or platinum lto 5 o Cadmium or zinc 5to20 Silverbalance The percentages are given by weight.

For the most desirable performance in electrical contacts cadmium is'generally to be pre- The specific proportions which have been found most suitable are as follows:

Percent Palladium or platinum 3 Cadmium 10' Silver balance 55 member, such as a rivet or disc, and the assembly heated to fuse the silver alloy to the backing.

The alloy has a melting point considerably higher than that'of silver and hence the resulting contacts are much lesssusceptible to sticking or 6 welding together due to over-heating from exis placed against the face of a steel backing cessive currents or inductive discharges through the mating contacts. I I

The surfaces of the contacts are also notably free from metal transfer or build-up as well aspitting. v

The contacts made from the present alloy are suitable for use with A. C. or D. C. and may be operated in pairs of the same compos tion or with a mating contact of entirely different composition such as a tungsten contact. Contacts of the above preferred composition have been operated with great success on high frequency electromagnetic vibrator-interrupters where the requirements are very exacting and tungsten contacts are usually required. These contacts have also been found suitable for, use in voltage regulators, relays and circuit breakers and shows a -definite improvement over fine silver and 'coin silver. g

The best method of determining the value of contacts is by the comparative operation under controlled conditions of the contacts under consideration with contacts of th'e prior art. Extensive comparison-tests have been madeon the contacts of an alloy of the present invention containing 87% silver, 10% cadmium and 3% palladium and contacts of fine silver (at least 99% silver), coin silver (90% silver, 10% copper) and a binary alloy of 80% silver and 20% cadmium.

The various contact materials were tested on Cutler-Hammer relays using one pair of contacts 0.187 diameter one of which was fiat faced and the other having approximately a 1" radius. The contacts were riveted on phosphor bronze reeds with the maximum opening about The frequency of operation was 1.4 seconds on, 1.4 seconds 011', making 1285 operations per hour. The load was resistive at a power factor of 100%. Tests were run at both 2 and 10 ounces total contact pressure. The test period consisted of '72 hours, of operation or in excess of 92,000 operations.

The following are some of the results obtained;

Sticking-The 80- 20 alloy, fine and coin silver contacts all stuck before the completion of the test period of 72 hours whereas the contact alloy of the present invention was still operating at the end of the test. Sticking occurred with the comparison alloys after the following number of operations:

Metal transfer and pittingmm silver showed the greatest tendencytoward pitting and transfer, followed in order, by the so-4o alloy and the alloy of the present invention. Coin silver was not compared in this regard.

Ozidation.The alloy of the present invention showed slightly less oxidation than the -20 alloy, fine silver or coin silver.

Contact wear.Contactwear is closely related to pitting and transfer. Therefore the comparison materials showed a tendency toward greater wear than the alloy of the present invention.

Contact resistance.--The change in contact resistance during operation is in general an indication of the operating characteristics of the contact material. An increasing contact resistance with length of operation indicates the formation of a high resistance oxide or a pitting or wearing oi the contact face. Increased resistance causes an increased tendency toward overheating and contact sticking.

The initial resistance of contacts made of the alloy of the present invention was lower than that of the 80-20 alloy and of coin silver. Fine silver generally has a lower initial resistance than all the others and remains constant on low current operation. However, its contact resistance increases very greatly with heavy loads frequently resulting in sticking.

The 8020 alloy showed a greater increase in resistance during operation than any others.

Coin silver showed a decrease. The alloy of the present invention was generally more constant with all current loads and with light and hes contact pressures.

It is contemplated that alloys containing normal amounts of impurities are within the scope oi the present invention.

While the present invention, as to its objects and advantages, has been described herein as carried out in specific embodiments thereof, it is not desired to be limited thereby but it is intended to cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is: v

1. An alloy composed of an element selected from the group consisting of palladium and platinum 1 to 5%, an element chosen from the group consisting or cadmium and zinc 5 to 20% and the remainder silver.

2. An alloy composed or! an element selected from the group consisting of palladium and platinum 1 to 5%, a cadmium 5 to 20% and the remainder silver.

3. An alloy composed of an element selected from the group consisting of palladium and platinum about 3%, cadmium about 10%, and the remainder silver.

4. An electrical contact member formed of an alloy composed of an element selected iron'r the group consisting of palladium and platinum l to 5%, an element chosen from the group consisting of cadmium and zinc 5 to 20% and the remainder silver.

5. An electrical contact member formed of an alloy composed of an element selected from the group consisting of palladium and platinum 1 to 5%, cadmium 5 to 20% and the remainder silver.

6. An electrical contact member formed of an alloy composed of an element selected from the group consisting of palladium and platinum about 3%, cadmium about 10%, and the remainder silver.

'7. An alloy containing about 1 to 5% of an element selected from the group consisting oi palladium and platinum, about 5 to 20% of an element selected from the group consisting of cadmium and zinc and the remainder substantially all silver, said alloy being characterized by a higher melting point than silver, less tendency toward oxidation than fine or coin silver, higher wear resistance than flne or coin silver, and greater constancy of operation in electric current control than fine silver, coin silver or a binary alloy of silver and cadmium.

8. An electrical contact member formed of an alloy containing about 1 to 5% of an element selected from the group consisting of palladium and platinum, about 5 to 20% of an element selected from the group consisting of cadmium and zinc and the remainder substantially all silver, said alloy being characterized by a higher melting point than silver, less tendency toward oxidation than fine or coin silver, higher wear resistance than flne or coin silver and greater constancy of operation in electric current control than rim:1 silver, coin silver or a binary alloy of all ,er an cadmium.

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